FIG. 8 is a perspective view showing a structure of a semiconductor device disclosed in Japanese Published Patent Application No. Sho. 64-89548. Referring to FIG. 8, a top ceramic frame 102 is calcined and mounted to a base ceramic 101. The package includes input and output leads 103 and 104, respectively, grounding leads 105 and 106 silver-soldered onto a grounding metallization layer 117 on the base ceramic 101, a semiconductor element 107 bonded to the grounding metallization layer 117 on the base ceramic 101, and a wire 108 formed of copper or the like electrically connecting an electrode (not shown) on the semiconductor element 107 to a metallization layer 116 for I/O terminals. A metallization layer 110 is provided on the top ceramic frame 102, cover 115 formed of metal is bonded to the metallization layer 110 by soldering or the like. In addition, inner and outer side wall metallizations 109a and 109b are provided on the inner and outer side walls of the top ceramic frame 102 over the grounding metallization layer 117, and a metallization layer 118 is provided on a back surface of the base ceramic 101. The semiconductor element 107 is connected to the metallization layer 118 through the grounding metallization layer 117 and a grounding metallization layer 112 on a side wall of the base ceramic 101 so as to be grounded. A metallization layer 116 provided on the base ceramic 101 is formed of a micro-wave strip line with a predetermined impedance. In addition, the width of the I/O leads 103 and 104 connected to the metallization layer 116 is the same as that of the metallization layer 116.
Next, an operation thereof will be described. A high-frequency input signal is input through the input lead 103 to the metallization layer 116 formed on the base ceramic 101, that is, the micro-wave strip line which can be used at the predetermined high frequency, and then input to the semiconductor element 107 through the wires 108. An output signal from the semiconductor element 107 is output to an external circuit (not shown) through the wires 108, the metallization layer 116 formed on the base ceramic 101, that is, the micro-wave strip line and the output lead 104.
Next, description will be given of a package. Since most of packages used in the conventional semiconductor device are entirely made of ceramic, the resonant frequency of the package is lowered and when it is used in a high-frequency semiconductor device, its characteristics are degraded. Therefore, lowering of the resonance frequency is prevented by providing the metallization layer 109a for electromagnetic shielding on the inner surface of the top ceramic 102 in the above-described semiconductor device.
Thus, according to the conventional semiconductor device of the above structure, since the base substrate is formed of ceramic having low heat conduction and undesirable heat dissipation properties, heat generated from the semiconductor element can not be effectively dissipated, which could cause destruction of the semiconductor element.